1. Field of the Invention
The present invention relates generally to busses for use in electronic devices.
2. Description of Related Art
The use of a bus to communicate between many devices is well known. Several standard busses include the AT-bus (or ISA-bus) in the IBM Corporation (Armonk, N.Y.) PC-AT, the VME bus in the Digital Equipment Corporation (Maynard, Md.) VAX line of computers, and the S-bus in workstations from Sun Microsystems Corporation (Fremont, Calif.). These busses were developed with certain design goals dictated by their use in microcomputer systems. Microprocessor computers typically only require high data transfers to and from a RAM. In general, except for these data-intensive communications with the RAM, the other devices on the bus generally communicate only with the system processor. Since the system processor often needs to communicate with several devices seemingly simultaneously, communication by the system processor is often performed in time division multiplex (TDM). In these types of busses, typically only one apparatus can use the bus at any given time. This is not a problem because quantities of information are generally small enough that the bus is not a bottleneck. Communication of large amounts of data to and from the RAM is generally accomplished through demand memory access (DMA), which allows bursts of data between certain devices and the RAM.
Busses such as these have been adopted for use in apparatuses other than computers. One application has been in network routers. Network routers exemplify the apparatuses which include a number of devices, each having substantially equal priority on the bus, each transferring similar quantities and qualities of data, and each needing to transfer data to any of the other devices. Network routers have been developed which include busses based upon the VME-bus and the S-bus. However, these routers and other data-transfer-intensive applications differ from computers because of the quantity of data to be transferred on the bus, the quality of that data, and the data's destination. As a consequence, these prior busses have often been inadequate to provide sufficient data throughput for many router applications.
One attempt to overcome this problem has been to provide multiple busses to increase the amount of data which can be transferred through the router. However, this approach can significantly increase the cost and complexity of the router.
Another approach has been to increase the clock frequency of the bus so that the data rate is increased. However, at high clock frequencies, harmful electromagnetic radiation can occur. As a result, increasing the clock frequency can often require substantially increased shielding to prevent undesirable electromagnetic interference (EMI).
Therefore, it is an object of the invention to provide a bus for use in high data transfer apparatuses.